It has been known heretofore to employ pressure compensating devices in conjunction with continuous integrators in order to obtain corrected volumetric gas measurements for meters. Such integrators frequently also provide for temperature compensation. For a complete disclosure of such a continuous integrator reference may be had to U.S. Pat. No. 3,538,766 granted Nov. 10, 1970. U.S. Pat. No. 3,780,580 granted Dec. 25, 1973 may also be referred to for a description of a prior art continuous integrator in which a pressure sensing element is interconnected with the integrator and in which both the pressure sensing element and the integrator have linear output motion as compared with earlier integrator assemblies in which one or more radial outputs resulted in the production of geometric error in converting the radial output to linear.
The pressure corrections applied to the integrator, as is well known, are based upon Boyle's law which may be expressed by the formula ##EQU1## WHERE Q is the volume of gas at a standard or base pressure, q represents the uncorrected volume of gas measured by the meter, A is the atmospheric pressure at the point of measurement in pounds absolute, p is the gage pressure and Pb is the standard or base pressure in pounds absolute. Thus, the volume of measured gas corrected to standard or base pressure will be seen to be a function of the ratio of absolute pressure at the point of measurement and at the desired standard or base pressure.
It has been appreciated prior to the present invention that compensation for fluctuations in atmospheric pressure at the location where volumetric measurement is being carried out is desirable. It becomes increasingly important to provide such compensation with measuring devices which operate in the low pressure range, i.e. 0-5 p.s.i.g. Changes in atmospheric pressure are attributable to (a) differences in elevation from one measuring site to another and (b) meteorological conditions at the site. The latter factor may vary constantly at a given site. Earlier attempts to provide such barometric compensation have required complex mechanism and frequently needed careful manual monitoring. There has, therefore, been a need for an integrator of the character described having the capability of automatic compensation for pressure variations including such as are attributable to atmospheric pressure changes.